Four types of regulation ammuniton were used by Civil War field artillery:

Solid Shot
Common Shell
Case Shot
Canister

Specimens of 12-pounder "grape shot" exist but this type of ammunition was more often used by siege and heavier weapons.

RE-ENACTMENT NOTE:
Obviously we do not fire live rounds on the re-enactment field. All that is put down the barrel of the cannon is a pre-packed, pre-measured charge of powder.